SainSmart 8 Channel DC 5V Relay with Step up converter.. flickering

Dear All,

I am building a smart sprinkler controller using the Spark Core. I connected Spark Core to a saintsmart 8 channel 5V relay. I wanted to drive the 24V solenoid using a step up converter that converts 5V (Spark Core VCC and GND) to 24V. I tested the output voltage and it is a stable 24V. Once I connect the circuit to the relay output and turn on the relay all the 8 relays start to flicker on-off, but when I use a separate power source (12V) to power the solenoids it works well.

the converter

What do you think the problem might be?

Another thing, I am testing using the Tinker app, once I connect the Spark Core to power all the 8 relays are powered on, how can I make it by default powered off when connected? I tried different relays and still the same thing. I am driving the relay from VCC and GND on the Spark Core.

Thank you for you help

How are you powering the spark core?

An external USB power supply I suppose? There’s a protection diode for the USB port and the max current should be 3A.

The relay coils draw quite a fair bit of current and the step up converter is unable to supply sufficiently.

Either the power supply needs to be beefier or the step up converter is simply unable to output enough current

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I am powering the core via USB. I used another USB input for the converter and it works well.

Thanks @kennethlimcp

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